In an atomic power plant, there is installed a moisture separator heater between a high-pressure steam turbine and a low-pressure steam turbine. The moisture separator heater separates moisture in steam exhausted from the high-pressure steam turbine and also reheats the steam from which moisture is separated to give high-temperature steam, reducing the degree of moisture of steam at the inlet of the low-pressure steam turbine, thereby attaining an improved heat efficiency of turbine plants.
An explanation will be made for one example of a structure of a conventional moisture separator heater by referring to FIG. 12 to FIG. 14. FIG. 12 is a perspective view of a moisture separator heating apparatus, and FIG. 13 is a front sectional view of the apparatus. FIG. 14 is a sectional view taken along line III-III of the moisture separator heating apparatus given in FIG. 13. Steam F1 exhausted from a high-pressure steam turbine (not illustrated) flows from a steam inlet portion 22 into the interior of a cylindrical body 21 at which the moisture separator heater is mounted transversely. The steam F1 which has flown into the body 21 is divided into two flows and introduced into cylindrical manifolds 23 arranged horizontally in a symmetrical manner, when the body 21 is viewed in section from the longitudinal direction (refer to FIG. 14).
The manifolds 23 are also called a pipe-type manifold and installed so as to be parallel to each other substantially across the entire length of the moisture separator heater in the longitudinal direction. The manifold 23 is provided with a plurality of slits 24 across the entire length of the manifold 23, and steam F1 inside the manifolds 23 is ejected from the slits 24 toward a steam reserving portion 25 installed at the lower part of the interior of the body 21. Further, the steam F1 ejected to the steam reserving portion 25 is separated from moisture in the course of passage through a separator 26 installed downstream thereof and flows into a steam collecting portion 27. In a sectional view of the body 21, the manifold 23, the steam reserving portion 25 and the separator 26 are arranged by one each in a symmetrical manner, and installed across the entire length of the body 21 in the longitudinal direction. The steam F1 which has flown into the steam collecting portion 27 through the separator 26 ascends to the steam collecting portion 27, flows into a heater 28 and is heated again by high-pressure extraction steam F2, which is a part of high-pressure steam. The heater 28 is a multi-tubular heat exchanger made up of many heating tubes 30 formed in a U tube shape. The high-pressure extraction steam F2 flows inside the tube of the heater and the steam F1 which ascends from the steam collecting portion 27 flows outside the tube of the heater. The steam F1 exchanges heat with the high-pressure extraction steam F2 via the heating tubes 30 and is thereby heated. The steam F1 which has passed through the heater 28 flows out from a steam outlet portion 29 installed at the upper part of the body and is then fed to a low-pressure steam turbine (not illustrated). The high-pressure extraction steam F2 is changed to drain F3 and exhausted from the heater 28. A specific example of the thus-explained moisture separator heater is disclosed in Patent Document 1 given below.
Further, Patent Document 2 given below shows a specific example of slits installed on a pipe-type manifold of a moisture separator heater. The steam-ejecting slits are changed in length and width, depending on the position of the manifold in the longitudinal direction and designed so as to obtain a uniform steam flow distribution across the entire length of the body 21 of the steam reserving portion 25 in the longitudinal direction and also in such a manner that the flow velocity of steam ejected from the slits 24 will not exceed a limit value. Where the flow velocity of steam exceeds the limit value, erosion will easily take place on the inner wall of the body 21. The slits 24 are made smaller in length and width as they are further spaced away from the upstream end of the manifold 23 nearer to the steam inlet portion 22 to the downstream end thereof, that is, as they are further spaced away from the upstream end, by which the opening area is gradually decreased. Since the slits are arranged as described above, it is possible to make uniform the flow distribution of steam flowing into the separator and the flow velocity of steam across the entire length of the separator.    PATENT DOCUMENT 1: Japanese Unexamined Patent Application, First Publication No. 2002-130609    PATENT DOCUMENT 2: Japanese Unexamined Patent Application, First Publication No. 2002-122303